Storage (recording) devices for information equipment mainly use a semiconductor memory or a magnetic memory. The semiconductor memory is typically used as an internal storage device in view of access time, whereas the magnetic disk drive is typically used as an external storage device in view of large capacity and nonvolatility. A memory capacity is an important index indicating the performance of a magnetic disk drive. Along with the recent development of information society, large capacity and small-sized magnetic disk drives are required by the market. A recording system suitable for the requirement is perpendicular recording. It is considered that the perpendicular recording becomes mainstream instead of the conventional longitudinal recording because high density can be promoted.
U.S. Patent Publication No. 2002/0176214 (“patent document 1”) discloses a perpendicular recording magnetic head that suppresses broadening of an unnecessary magnetic field across track width by disposing a soft magnetic film on both sides of a main pole in the track-width direction. Japanese Patent Publication No. 2006-164356 (“patent document 2”) discloses a perpendicular recording magnetic head that prevents a stray magnetic field from concentrating on a magnetic head element by the following. A soft magnetic shield is provided to surround the upper portion and lateral sides of the magnetic head element, thereby making the distance between the soft magnetic shield and a medium smaller than that between the soft magnetic shield and the magnetic head element.
The magnetization direction of a recording medium of perpendicular recording is perpendicular to the surface of the medium; therefore, an effect of demagnetizing field acting between adjacent magnetic domains in the recording medium of perpendicular recording is smaller than that of longitudinal recording. For this reason, high-density magnetic information can be recorded in the medium, which makes it possible to construct a large capacity magnetic disk.
In perpendicular recording, a main pole has a flare point and magnetic flux is restricted at the flare point to generate a strong magnetic field. A write field from the main pole has an effect on a track-width direction as well as on a continuously recording bit-direction. Since adjacent bit information is written in the track-width direction, there is a problem in that an extremely strong magnetic field erases the magnetic information outside a write area during write operation. Patent documents 1 and 2 mentioned above describe head configurations to solve such a problem.
It was confirmed by computational simulation that the technique described in patent document 1 can enable objective recording quality and retainment of adjacent recording information. However, the following was found in order to satisfy the objective. It is necessary that the backward length of the soft magnetic film provided on both sides of and close to the main pole is set to an extremely short length (50 to 200 nm) with a high degree of accuracy (±10 nm). In addition, it is necessary that the flare point of the main pole is set to 50 to 200 nm with a high degree of accuracy (±10 nm) in order to generate a strong magnetic field. It was found that the formation accuracy (film thickness and backward length) of such members needs to be set at as extremely accurate as a range of ±10 nm in order to achieve high quality recording operation as an objective. Thus, if perpendicular recording heads were manufactured by the commercially available semiconductor manufacturing equipment, manufacturing yield was low so that inexpensive heads could not be mass-produced.
According to the technique described in patent document 2, since the end of the soft magnetic shield is disposed at a position spaced extremely apart from the main pole (1 μm or more), an effect of suppressing the broadening of the magnetic field across the track-width is insufficient.
In order to achieve this effect, it is necessary to set the formation accuracy of members forming the head at an extremely high level. In the case of manufacturing perpendicular recording heads by commercially available manufacturing equipment, a manufacturing yield is low so that inexpensive heads cannot be mass-produced.